Chen Mingdong (left), a suspect in the murder of a mother and four children in Brooklyn, is escorted by police on Sunday. Photo: AP

The phone calls came in rapid succession, each call more frantic than the last, made by a woman intent on warning her relatives that her husband's 25-year-old Chinese cousin, who had been staying with their family only a few days, was not acting right.

But by the time her family members could stop by her home in Brooklyn on Saturday, it was too late. Inside the apartment, the woman, Qiao Zhen Li, lay unconscious in the kitchen, next to her five-year-old son, Kevin Zhuo; both were mortally wounded. The bodies of her three other children, all stabbed to death, were in a rear bedroom.

"They bang on the door and they bang on the door," Chief Philip Banks, the Police Department's highest-ranking uniformed officer, said of Li's relatives. When they finally got inside on Saturday night, they came upon the carnage, and the man believed to be responsible, Chen Mingdong, covered in blood.

A police source told the New York Post that the youngest child, aged one, was decapitated.

Chen, the cousin, was charged on Sunday with five counts of murder. He was also charged with assaulting a police officer and resisting arrest; authorities said he had attacked an officer in the 66th Precinct station house while being processed.

The killings tore through the family like a fire: sudden and complete. The five murders in the three-room home in the Sunset Park neighbourhood, where the children and their parents enjoyed a seemingly ordinary life, the police said, stood out for their brutality and magnitude.

It was "not something that has been seen before in recent memory", said John McCarthy, the Police Department's chief spokesman.

Banks said the scene was one seared into his memory. He called the crime an "unspeakable act" on a "normal family".

That very New York normality appeared to grate on Chen, who lived an impoverished and itinerant life between Chinatown in Manhattan, Chicago and most recently, his cousin's home in Sunset Park. Under interrogation by detectives, conducted in Putonghua, he told of his disillusionment with life since coming to the United States in 2004 and of his jealousy towards those who had found success in the country. The police listed him as unemployed, and media reports said he was an illegal alien.

But it remained unclear exactly what prompted him to turn his rage on his cousin's wife, Li, 37, and their four children, identified by the police as Linda, nine; Amy, seven; Kevin, five; and William, one. The police said Chen appeared to have stayed with them before without incident.

The family did not appear to be better off than those who lived around them in their Chinese enclave in Brooklyn, neighbours said. They sent their three school-aged children to a local public school, the Education Department said. Li stayed at home with William. The authorities had no record of trouble in the household.

May Chee, a neighbour of the family who grew up on the block, said she often saw Li outside with her children, who would chase one another and play with the other children living along 57th Street, a block teeming with young people.

Li watched over them from her front step, often chatting on her cellphone, Chee said, adding that the mother did not speak much English.

Few in the area recalled Chen, who had only recently arrived there. A woman who lives next to the family and gave her name only as Ms Zheng said she had seen the cousin in recent days standing outside the two-storey, two-family home, smoking cigarettes and talking on the phone. A cousin of the mother, Yun Gao, 29, said Chen was emotionally unstable. She did not elaborate.

The only weapon used in the killings, the police said, was a large kitchen knife, described by the authorities as a meat cleaver. Banks said that the bodies "were cut and butchered" and that most of the wounds were to the neck and torso.

Chee said she saw the children's father, Yi Lin Zhuo, 31, arrive after the police cars on Saturday night. "He was crying," she said. "He was screaming."

Two women arrived with him, one of them weeping.

"It's so sad," Chee said. "The only thing I can do is pray for them, pray for the family. It's crazy. You don't kill kids. Don't take it out on the kids."

Chen had no prior arrests in New York, the police said, and did not appear to have had trouble with the law in Chicago.

During the interrogation, Chen spoke in general of feelings of resentment, the police said. "He made a very soft comment that since he's been in this country, everyone seems to be doing better than him," Banks said.

"We're not really sure what that means. But that is the only thing that we have now. We're still looking into it."

This article appeared in the South China Morning Post print edition as Slain for living a normal, happy life